Prior co-pending applications Ser. No. 06/565,540, filed Dec. 27, 1983, and Ser. No. 06/589,640 filed Mar. 14, 1984, now abandoned, both assigned to the assignee herein, disclose a viscous product dispenser utilizing a free-floating take-up piston which automatically responds to the discharge of a volume of product from the dispenser by moving under the influence of atmospheric pressure to "take-up" the space in the chamber left vacant by the discharged product. It has been found that in isolated circumstances during shipment or other handling of the dispenser, a sharp blow to the dispenser may result in the take-up piston inching forwardly in the product chamber by a small increment, nothwithstanding the fact that the actuating lever has not been depressed. Because the take-up piston is provided with one-way retaining structure which prevents it from moving in a reverse direction, once the take-up piston has been jarred forwardly, it applies an additional loading pressure to the contents and encourages at least a minimal amount of seepage from the discharge spout of the dispenser. This can occur to a certain extent even though the actuating lever as disclosed in such prior applications is provided with a shutoff valve flap integral therewith that covers the outlet of the spout during periods of nonuse.